1. Field of the Invention
The present invention relates generally to methods for controlling the formation of films in semiconductor processing. More particularly, the present invention relates to controlling the wafer edge film thickness profile in atmospheric pressure CVD processes.
2. Description of the Related Art
In a conventional deposition process such as atmospheric pressure (ATM-P) chemical vapor deposition (CVD) process, a deposition gas is supplied through a shower head. After heating causes the wafer to reach the process temperature, film deposition occurs on the wafer. For example, an oxidation film may grow on the surface of the wafer when exposed to an oxidizing precursor.
The uniformity of the film thickness depends upon a constant gas flow and uniform temperature on the wafer. Even though control of these main process parameters may generally provide uniformity in the film thickness across most of the wafer, the conventional method typically results in a film thicker at the wafer edge than the inner portions of the wafer.
Accordingly, what is needed is a process or apparatus that will provide a controlled uniform film thickness on the wafer edge during the ATM-P CVD process.
The present invention provides a process and apparatus for controlling the thickness of a film at the wafer edge during an atmospheric pressure (ATM-P) chemical vapor deposition process. The present invention exploits the fact that the film thickness at a particular wafer location may correspond to the density of the deposition gases in that wafer area. In particular, the density of the flow gases is modified in the area surrounding the wafer edge. In order to achieve uniformity of film thickness at the wafer edge, the present invention provides an apparatus and a process whereby a ring shaped gas flow control device is placed so as to surround the wafer. The height of the ring may be changed to control the growth rate on the wafer edge. In one embodiment placing the top surface of the ring higher than the wafer surface reduces the growth rate. In another embodiment placing the top surface of the ring lower than the wafer top surface increases the growth rate. Atmospheric pressure CVD refers to systems whose deposition environment operates at or near atmospheric pressure. Typically, the gas flow, temperature, and exposure time in the deposition zone determine the film thickness.
In one aspect, a chemical vapor deposition system for controlling a film thickness deposited at a wafer edge is provided. The system comprises a wafer holder for supporting a wafer and a gas flow control ring disposed on the wafer holder. The gas control ring is configured to surround the wafer and has a top surface arranged at a height relative to the top surface of the wafer to control the deposited film thickness at the wafer edge. In one aspect, the height of the top surface of the ring is in the same plane as the top surface of the wafer. The inner diameter of the gas flow control ring has a clearance relative to the periphery of the wafer of less than one mm. In another aspect, the height of the gas flow control ring top surface is higher than the top surface of the wafer.
In yet another aspect, the height of the gas flow control ring top surface is lower than the top surface of the wafer.
These and other features and advantages of the present invention are described below with reference to the drawings.